README.md

@@ -132,7 +132,7 @@ partial, alternate, and planned behavior.
 | `--existing` | Skip files not already present at the destination; update existing files normally. |
 | `--bwlimit <KB/s>` | Bandwidth limit in kilobytes per second |
 | `--chunk-size <n>` | Chunk size in bytes (default: 10485760) |
-| `--timeout <sec>` | I/O timeout in seconds. Applied to both the socket (`SO_RCVTIMEO`/`SO_SNDTIMEO`, built-in default 30 s) and the per-message protocol poll deadline (built-in default 60 s). `0` (the default/unset sentinel) keeps both built-ins; a positive value overrides both. |
+| `--timeout <sec>` | Positive I/O timeout in seconds, applied to both the socket (`SO_RCVTIMEO`/`SO_SNDTIMEO`, built-in default 30 s) and the per-message protocol poll deadline (built-in default 60 s). Omit the option to keep both built-ins; `0` is rejected. The server side keeps the built-in 60 s protocol window (the value is not sent on the wire). |
 | `--contimeout <sec>` | Connection timeout in seconds (default: 10) |
 | `--backup` | Backup existing destination files before overwriting |
 | `--backup-dir <dir>` | Target directory for backups (requires `--backup`) |
@@ -155,10 +155,14 @@ partial, alternate, and planned behavior.
 send/receive (the `poll()` deadline), so a peer that stops mid-frame is dropped. It
 does not, by itself, stop a peer that keeps sending well-formed frames forever. The
 receiver therefore also enforces two wall-clock (`CLOCK_MONOTONIC`) bounds on a
-connection: a **1 hour** idle limit (only `STATUS_KEEPALIVE`/`STATUS_ABORT` frames
-seen for that long counts as no forward progress) and a **24 hour** overall session
-cap. Both are deliberately generous so a legitimate long-running transfer is never
-aborted; they exist to defeat keepalive slowloris squatting on a connection slot.
+connection: a **1 hour** idle limit and a **24 hour** overall session cap. Only
+frames that move real work (not `STATUS_KEEPALIVE`/`STATUS_ABORT` and not an
+empty `STATUS_CHECK_BATCH`/`STATUS_DIR_TIMES`) refresh the idle timestamp, so a
+peer cannot hold a connection slot by emitting cheap empty frames; a peer that
+fabricates minimal non-empty frames can still occupy a slot until the 24 hour
+cap, since no bound can require actual payload without risking a legitimate
+long operation. Both are deliberately generous so a legitimate long-running
+transfer is never aborted.
 
 ### Server
 
@@ -393,7 +397,7 @@ features without changing the meaning of ordinary compatibility options.
 | `--bwlimit <KB/s>` | Apply token-bucket bandwidth limiting. |
 | `--progress` | Show transfer progress and throughput. |
 | `--stats` | Print transfer statistics. |
-| `--timeout <seconds>` | Set the socket **and** per-message protocol I/O timeout. `0` keeps the built-in 30 s socket / 60 s protocol defaults; a positive value overrides both. |
+| `--timeout <seconds>` | Set the socket **and** per-message protocol I/O timeout (positive seconds). Omit to keep the built-in 30 s socket / 60 s protocol defaults. |
 | `--contimeout <seconds>` | Set connection timeout. |
 
 Short-option conflicts with rsync have been resolved for the CLI namespace

src/server/receiver.c

@@ -203,22 +203,41 @@ bool receiver_time_limit_exceeded(const struct timespec* session_start,
   return false;
 }
 
+/* A frame proves forward progress only when it cannot be fabricated for free.
+ * KEEPALIVE/ABORT are pure liveness, and CHECK_BATCH/DIR_TIMES may carry zero
+ * entries, so a peer must not be able to hold a connection slot forever by
+ * merely emitting empty frames. */
+static bool status_counts_as_progress(Status status) {
+  switch (status) {
+  case STATUS_KEEPALIVE:
+  case STATUS_ABORT:
+  case STATUS_CHECK_BATCH:
+  case STATUS_DIR_TIMES:
+    return false;
+  default:
+    return true;
+  }
+}
+
 /* Refresh the progress timestamp for a forward-moving frame and enforce the
- * bounds above.  Returns false (after best-effort STATUS_ERROR) when the
- * connection must be dropped. */
+ * bounds above.  Returns false when the connection must be dropped; the
+ * terminal STATUS_ERROR is sent only when the sink owns error reporting (the
+ * -m sink sets send_error=false so the main thread emits exactly one). */
 static bool receiver_note_status(const struct timespec* session_start,
-                                 struct timespec* last_progress, Status status,
-                                 int file_descriptor) {
+                                 struct timespec* last_progress, Status status, int file_descriptor,
+                                 const ReceiverSink* sink) {
   struct timespec now;
-  clock_gettime(CLOCK_MONOTONIC, &now);
-  if (status != STATUS_KEEPALIVE && status != STATUS_ABORT)
+  if (clock_gettime(CLOCK_MONOTONIC, &now) != 0)
+    now = *last_progress;
+  if (status_counts_as_progress(status))
     *last_progress = now;
   if (!receiver_time_limit_exceeded(session_start, last_progress, &now))
     return true;
   log_message(LOG_LEVEL_ERROR,
               "Receive session exceeded its time bound (idle %us / total %us); aborting connection",
               g_max_session_idle_sec, g_max_session_wall_sec);
-  send_status(file_descriptor, STATUS_ERROR);
+  if (!sink || sink->send_error)
+    send_status(file_descriptor, STATUS_ERROR);
   return false;
 }
 
@@ -248,7 +267,7 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
   struct timespec last_progress;
   clock_gettime(CLOCK_MONOTONIC, &session_start);
   last_progress = session_start;
-  if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor))
+  if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor, sink))
     return -1;
   bool early_delete = config_delete_timing_early(config);
   /* Parked keep-set for the late/commit timing.  Every exit path below frees it
@@ -349,7 +368,7 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
   next_status:
     if (!receive_status(file_descriptor, &status))
       goto receive_error;
-    if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor))
+    if (!receiver_note_status(&session_start, &last_progress, status, file_descriptor, sink))
       goto fail;
   }
   if (status != STATUS_FINISHED) {

src/server/server.c

@@ -609,10 +609,11 @@ void handler(int file_descriptor) {
   if (gate_ctx.super_mode_override != -1)
     config->super_mode = (SuperMode)gate_ctx.super_mode_override;
   protocol_set_8_bit_output(config->eight_bit_output);
-  /* Honor the negotiated --timeout for every protocol frame from here on (the
-   * config handshake itself used the built-in 60 s window).  A positive value
-   * also tightens the socket SO_RCVTIMEO/SO_SNDTIMEO already applied by the
-   * transport; 0 leaves both built-in defaults in place. */
+  /* Server-side per-message protocol deadline for every frame from here on.
+   * `timeout` is not serialized, so this is the server's own config (the server
+   * has no --timeout CLI and defaults it to 0): the built-in 60 s window stays
+   * in effect.  A client's --timeout tightens only that client's own protocol
+   * I/O and the server's socket read/write timeout is the transport default. */
   protocol_session_set_io_timeout(&session, config->timeout);
   if (!authorized_root) {
     log_message(LOG_LEVEL_ERROR, "No server-side destination root configured");

src/shared/file_send.c

@@ -145,7 +145,7 @@ bool file_send_sendfile_with_skip(File* file, int file_descriptor, bool use_meta
   off_t offset = 0;
   struct timespec deadline;
   clock_gettime(CLOCK_MONOTONIC, &deadline);
-  deadline.tv_sec += 60;
+  deadline.tv_sec += protocol_get_io_timeout_sec();
   while ((unsigned long long)offset < file_size) {
     struct timespec now;
     clock_gettime(CLOCK_MONOTONIC, &now);

src/shared/protocol.c

@@ -87,6 +87,12 @@ void protocol_session_set_io_timeout(ProtocolSession* session, int sec) {
   session->io_timeout_sec = sec;
 }
 
+int protocol_get_io_timeout_sec(void) {
+  const ProtocolSession* session = bound_session ? bound_session : &legacy_io_session;
+  int sec = session->io_timeout_sec;
+  return sec > 0 ? sec : RECEIVE_TIMEOUT_SEC;
+}
+
 void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long max_alloc) {
   if (!session)
     session = bound_session ? bound_session : &legacy_io_session;

src/shared/protocol.h

@@ -152,6 +152,10 @@ void protocol_session_set_max_alloc(ProtocolSession* session, unsigned long long
  * An explicit long deadline (e.g. the delete-ack wait) is applied per-call by
  * protocol_receive_status_timed and is unaffected by this setter. */
 void protocol_session_set_io_timeout(ProtocolSession* session, int sec);
+/* Effective per-message I/O deadline (seconds) for the currently-bound session,
+ * falling back to the built-in default.  Used by the plaintext sendfile path
+ * which bypasses the protocol send primitive. */
+int protocol_get_io_timeout_sec(void);
 void* protocol_alloc(size_t size);
 void* protocol_realloc(void* ptr, size_t size);
 void protocol_session_set_8_bit_output(ProtocolSession* session, bool enabled);

tests/test_receiver_timeout.c

@@ -62,19 +62,28 @@ static void test_receiver_aborts_idle_keepalive() {
   protocol_session_bind(&session);
 
   Status keepalive = STATUS_KEEPALIVE;
-  EXPECT_EQ_INT((int)write(sv[0], &keepalive, sizeof(keepalive)), (int)sizeof(keepalive));
-  int result = receiver_process_pending(config, sv[1], &sink, NULL);
-  EXPECT_EQ_INT(result, -1);
-
+  ssize_t wrote = write(sv[0], &keepalive, sizeof(keepalive));
+  int result = -2;
+  if (wrote == (ssize_t)sizeof(keepalive))
+    result = receiver_process_pending(config, sv[1], &sink, NULL);
   Status reply = STATUS_OK;
-  EXPECT_EQ_INT((int)read(sv[0], &reply, sizeof(reply)), (int)sizeof(reply));
-  EXPECT_EQ_INT((int)reply, (int)STATUS_ERROR);
+  ssize_t got = -1;
+  if (result == -1)
+    got = read(sv[0], &reply, sizeof(reply));
 
+  /* Tear down the binding/descriptors BEFORE asserting: an EXPECT_* failure
+   * returns immediately, and a dangling bound_session would poison later
+   * fd-level protocol I/O tests. */
   protocol_session_unbind();
   config_delete(config);
   close(sv[0]);
   close(sv[1]);
   receiver_reset_time_limits();
+
+  EXPECT_EQ_INT((int)wrote, (int)sizeof(keepalive));
+  EXPECT_EQ_INT(result, -1);
+  EXPECT_EQ_INT((int)got, (int)sizeof(reply));
+  EXPECT_EQ_INT((int)reply, (int)STATUS_ERROR);
 }
 
 void test_receiver_timeout(void) {